BitVec
This introduces lemma support for BitVec.ofInt/BitVec.toInt as well as lemmas upstreamed from Std and Mathlib for reasoning about emod and bmod.
These still need tests, but I thought I'd upstream so I can use benchmarking and check for build errors.
This is pretty big PR that upstreams all of Std.Data.Int.Init in one go. So far lemmas have seen minimal changes needed to adapt to Lean core environment. --------- Co-authored-by: Scott Morrison <scott.morrison@gmail.com>
